_Black_ is a well-behaved Unix-style command-line tool:
-- it does nothing if no sources are passed to it;
+- it does nothing if it finds no sources to format;
- it will read from standard input and write to standard output if `-` is used as the
filename;
- it only outputs messages to users on standard error;
-- exits with code 0 unless an internal error occurred (or `--check` was used).
+- exits with code 0 unless an internal error occurred or a CLI option prompted it.
## Usage
### Command line options
-_Black_ has quite a few knobs these days, although _Black_ is opinionated so style
-configuration options are deliberately limited and rarely added. You can list them by
-running `black --help`.
+The CLI options of _Black_ can be displayed by expanding the view below or by running
+`black --help`. While _Black_ has quite a few knobs these days, it is still opinionated
+so style options are deliberately limited and rarely added.
<details>
-<summary>Help output</summary>
+<summary>CLI reference</summary>
+
+```{program-output} black --help
-```
- Usage: black [OPTIONS] [SRC]...
-
- The uncompromising code formatter.
-
- Options:
- -c, --code TEXT Format the code passed in as a string.
- -l, --line-length INTEGER How many characters per line to allow.
- [default: 88]
-
- -t, --target-version [py27|py33|py34|py35|py36|py37|py38|py39]
- Python versions that should be supported by
- Black's output. [default: per-file auto-
- detection]
-
- --pyi Format all input files like typing stubs
- regardless of file extension (useful when
- piping source on standard input).
-
- -S, --skip-string-normalization
- Don't normalize string quotes or prefixes.
- -C, --skip-magic-trailing-comma
- Don't use trailing commas as a reason to
- split lines.
-
- --check Don't write the files back, just return the
- status. Return code 0 means nothing would
- change. Return code 1 means some files
- would be reformatted. Return code 123 means
- there was an internal error.
-
- --diff Don't write the files back, just output a
- diff for each file on stdout.
-
- --color / --no-color Show colored diff. Only applies when
- `--diff` is given.
-
- --fast / --safe If --fast given, skip temporary sanity
- checks. [default: --safe]
-
- --include TEXT A regular expression that matches files and
- directories that should be included on
- recursive searches. An empty value means
- all files are included regardless of the
- name. Use forward slashes for directories
- on all platforms (Windows, too). Exclusions
- are calculated first, inclusions later.
- [default: \.pyi?$]
-
- --exclude TEXT A regular expression that matches files and
- directories that should be excluded on
- recursive searches. An empty value means no
- paths are excluded. Use forward slashes for
- directories on all platforms (Windows, too).
- Exclusions are calculated first, inclusions
- later. [default: /(\.direnv|\.eggs|\.git|\.
- hg|\.mypy_cache|\.nox|\.tox|\.venv|venv|\.svn|_bu
- ild|buck-out|build|dist)/]
-
- --extend-exclude TEXT Like --exclude, but adds additional files
- and directories on top of the excluded
- ones (useful if you simply want to add to
- the default).
-
- --force-exclude TEXT Like --exclude, but files and directories
- matching this regex will be excluded even
- when they are passed explicitly as
- arguments.
-
-
- --stdin-filename TEXT The name of the file when passing it through
- stdin. Useful to make sure Black will
- respect --force-exclude option on some
- editors that rely on using stdin.
-
- -q, --quiet Don't emit non-error messages to stderr.
- Errors are still emitted; silence those with
- 2>/dev/null.
-
- -v, --verbose Also emit messages to stderr about files
- that were not changed or were ignored due to
- exclusion patterns.
-
- --version Show the version and exit.
- --config FILE Read configuration from FILE path.
- -h, --help Show this message and exit.
```
</details>
+Note that all command-line options listed above can also be configured using a
+`pyproject.toml` file (more on that below).
+
+### Code input alternatives
+
+#### Standard Input
+
+_Black_ supports formatting code via stdin, with the result being printed to stdout.
+Just let _Black_ know with `-` as the path.
+
+```console
+$ echo "print ( 'hello, world' )" | black -
+print("hello, world")
+reformatted -
+All done! ✨ 🍰 ✨
+1 file reformatted.
+```
+
+**Tip:** if you need _Black_ to treat stdin input as a file passed directly via the CLI,
+use `--stdin-filename`. Useful to make sure _Black_ will respect the `--force-exclude`
+option on some editors that rely on using stdin.
+
+#### As a string
+
+You can also pass code as a string using the `-c` / `--code` option.
+
+```console
+$ black --code "print ( 'hello, world' )"
+print("hello, world")
+```
+
+### Writeback and reporting
+
+By default _Black_ reformats the files given and/or found in place. Sometimes you need
+_Black_ to just tell you what it _would_ do without actually rewriting the Python files.
+
+There's two variations to this mode that are independently enabled by their respective
+flags. Both variations can be enabled at once.
+
+(labels/exit-code)=
+
+#### Exit code
+
+Passing `--check` will make _Black_ exit with:
+
+- code 0 if nothing would change;
+- code 1 if some files would be reformatted; or
+- code 123 if there was an internal error
+
+```console
+$ black test.py --check
+All done! ✨ 🍰 ✨
+1 file would be left unchanged.
+$ echo $?
+0
+
+$ black test.py --check
+would reformat test.py
+Oh no! 💥 💔 💥
+1 file would be reformatted.
+$ echo $?
+1
+
+$ black test.py --check
+error: cannot format test.py: INTERNAL ERROR: Black produced code that is not equivalent to the source. Please report a bug on https://github.com/psf/black/issues. This diff might be helpful: /tmp/blk_kjdr1oog.log
+Oh no! 💥 💔 💥
+1 file would fail to reformat.
+$ echo $?
+123
+```
+
+#### Diffs
+
+Passing `--diff` will make _Black_ print out diffs that indicate what changes _Black_
+would've made. They are printed to stdout so capturing them is simple.
+
+If you'd like colored diffs, you can enable them with the `--color`.
+
+```console
+$ black test.py --diff
+--- test.py 2021-03-08 22:23:40.848954 +0000
++++ test.py 2021-03-08 22:23:47.126319 +0000
+@@ -1 +1 @@
+-print ( 'hello, world' )
++print("hello, world")
+would reformat test.py
+All done! ✨ 🍰 ✨
+1 file would be reformatted.
+```
+
+### Output verbosity
+
+_Black_ in general tries to produce the right amount of output, balancing between
+usefulness and conciseness. By default, _Black_ emits files modified and error messages,
+plus a short summary.
+
+```console
+$ black src/
+error: cannot format src/black_primer/cli.py: Cannot parse: 5:6: mport asyncio
+reformatted src/black_primer/lib.py
+reformatted src/blackd/__init__.py
+reformatted src/black/__init__.py
+Oh no! 💥 💔 💥
+3 files reformatted, 2 files left unchanged, 1 file failed to reformat.
+```
+
+Passing `-v` / `--verbose` will cause _Black_ to also emit messages about files that
+were not changed or were ignored due to exclusion patterns. If _Black_ is using a
+configuration file, a blue message detailing which one it is using will be emitted.
+
+```console
+$ black src/ -v
+Using configuration from /tmp/pyproject.toml.
+src/blib2to3 ignored: matches the --extend-exclude regular expression
+src/_black_version.py wasn't modified on disk since last run.
+src/black/__main__.py wasn't modified on disk since last run.
+error: cannot format src/black_primer/cli.py: Cannot parse: 5:6: mport asyncio
+reformatted src/black_primer/lib.py
+reformatted src/blackd/__init__.py
+reformatted src/black/__init__.py
+Oh no! 💥 💔 💥
+3 files reformatted, 2 files left unchanged, 1 file failed to reformat
+```
+
+Passing `-q` / `--quiet` will cause _Black_ to stop emitting all non-critial output.
+Error messages will still be emitted (which can silenced by `2>/dev/null`).
+
+```console
+$ black src/ -q
+error: cannot format src/black_primer/cli.py: Cannot parse: 5:6: mport asyncio
+```
+
+### Versions
+
+You can check the version of _Black_ you have installed using the `--version` flag.
+
+```console
+$ black --version
+black, version 23.3.0
+```
+
+An option to require a specific version to be running is also provided.
+
+```console
+$ black --required-version 21.9b0 -c "format = 'this'"
+format = "this"
+$ black --required-version 31.5b2 -c "still = 'beta?!'"
+Oh no! 💥 💔 💥 The required version does not match the running version!
+```
+
+This is useful for example when running _Black_ in multiple environments that haven't
+necessarily installed the correct version. This option can be set in a configuration
+file for consistent results across environments.
+
## Configuration via a file
_Black_ is able to read project-specific default values for its command line options
[PEP 518](https://www.python.org/dev/peps/pep-0518/) defines `pyproject.toml` as a
configuration file to store build system requirements for Python projects. With the help
-of tools like [Poetry](https://python-poetry.org/) or
-[Flit](https://flit.readthedocs.io/en/latest/) it can fully replace the need for
-`setup.py` and `setup.cfg` files.
+of tools like [Poetry](https://python-poetry.org/),
+[Flit](https://flit.readthedocs.io/en/latest/), or
+[Hatch](https://hatch.pypa.io/latest/) it can fully replace the need for `setup.py` and
+`setup.cfg` files.
### Where _Black_ looks for the file
line-length = 88
target-version = ['py37']
include = '\.pyi?$'
+# 'extend-exclude' excludes files or directories in addition to the defaults
extend-exclude = '''
# A regex preceded with ^/ will apply only to files and directories
# in the root of the project.
-^/foo.py # exclude a file named foo.py in the root of the project (in addition to the defaults)
+(
+ ^/foo.py # exclude a file named foo.py in the root of the project
+ | .*_pb2.py # exclude autogenerated Protocol Buffer files anywhere in the project
+)
'''
```
## Next steps
-You've probably noted that not all of the options you can pass to _Black_ have been
-covered. Don't worry, the rest will be covered in a later section.
-
A good next step would be configuring auto-discovery so `black .` is all you need
instead of laborously listing every file or directory. You can get started by heading
over to [File collection and discovery](./file_collection_and_discovery.md).
projects / etc / vim.git / blobdiff